This invention relates to discharging a superconducting magnet at a substantially constant voltage.
Non-cryostable superconducting magnets can develop resistive zones (or xe2x80x9cquenchesxe2x80x9d) in their interiors. If such a zone develops, high levels of energy, in particular current, in the magnet can cause the magnet severe damage. Systems therefore have been developed for discharging superconducting magnets in an attempt to avoid such damage. The foregoing is familiar to those skilled in the art of designing and fabricating superconducting magnets.
The invention is directed to discharging a superconducting magnet. In general, in one aspect, the invention features a method which detects a quench in the superconducting magnet, and which discharges the superconducting magnet into a load at a substantially constant voltage in response to detecting the quench.
Discharging the magnet at a substantially constant voltage decreases discharging time (relative to constant power or constant resistance discharge). As a result, the likelihood (and/or amount) of damage to the magnet can be reduced. Also, if the magnet is connected to a utility system, for example, through an inverter, discharging the magnet at a substantially constant voltage increases the rate at which power can be supplied to the utility network. As a result, the utility network can be stabilized more quickly following a fault.
This aspect of the invention may include one or more of the following features. The voltage may be discharged through an inverter arranged between the superconducting magnet and the load. An input of the inverter receives voltage from an output of the superconducting magnet, and the substantially constant voltage is maintained at the input of the inverter by controlling a phase relationship between voltage and current at an output of the inverter. The inverter may be operated in overload mode during constant voltage discharge. Operating the inverter in overload mode further decreases magnet discharging time.
The load may comprise a utility network and/or one or more resistive elements. One of the advantages of discharging the magnet into a utility network is that it reduces the need for additional circuitry for discharging the magnet. The quench is detected by monitoring a superconducting coil in the superconducting magnet. Discharging generally occurs until an amount of energy in the superconducting magnet is below a predetermined level. This reduces damage to the magnet. The magnet may also be discharged into a load having a substantially constant resistance. This may be done after the magnet has been discharged at the substantially constant voltage, e.g., when the magnet is no longer in serious danger of damage.
Other advantages and features of the invention will become apparent from the following description and claims.